There are tools for defense at the play of cards, including Duplicate
Bridge.
Most Tools Are
Ancient. Surprisingly,
many have been known and refined for centuries - much longer than bridge has
existed as a game. They work well, but they must be learned and applied constantly.
Because they are less dramatic than bidding or declarer play, they are
often not used well by defenders, especially those who are looking to get on with the next
hand so they can bid and declare. This is a real attitude problem if you want to
play bridge well. Defense is bridge; Bridge is
Defense.
Generally, tools fall into these categories. Each is explained in
some detail elsewhere.
Visualization
is mentally seeing all the cards in all four hands and determining the declarer's best
line of play and your best line of defense.
Planning the
Defense is
your deliberate effort to defeat a contract or hold declarer to the minimum number of
tricks. This is the essence of Duplicate -- without a Defensive Plan, it's just tossing in
cards.
Counting
refers to everything you can count: HCP's, cards, tricks, distributions, matchpoints.
Signals are
the only legitimate communication with your partner while defending: if you don't use them
- and properly - you've cut off your own communications and your only ally -- and declarer
will win going away.
Leads are
one of the most potent tools for the defense, as you get to lead first. That starts the
defensive campaign, and is the single act most likely to defeat a close contract.